Natural gas, which is used by household consumers, is composed primarily of methane. Prior to use, it must be filtered, stripped of crude oil and other higher boiling alkanes (e.g. ethane, propane, or pentane), dehydrated, and “sweetened”, whereby CO2 and H2S are removed from the natural gas. Amongst these purification steps, both 1) the dehydration step and 2) the “sweetening” step could benefit significantly from using purification agents with increased surface area.
In the dehydration step, the gas is treated with ethylene glycols (mono-, di-, tri-, etc.) to remove water. Due to the high affinity of glycols for water, the wet gas that flows through a ‘contactor’, which is in essence a tower packed with mesh or bubble cap trays that maximize contact between the glycol (dessicant) and the gas, is dried through its interaction with the glycols.
The removal of acid gases from raw natural gas is referred to as “gas sweetening”. Raw natural gas typically contains far higher levels of CO2 and H2S than are allowed in the final product. The corrosive nature of the acidic gases and the toxicity of H2S are amongst the principle reasons for minimization of their contamination in natural gases. During the gas “sweetening” step, where H2S and CO2 are removed, the gas flows through an amine-containing contactor or through a column of agitated amine solution. The amine absorbs and reacts with H2S and CO2, thus removing the acidic gases from the gas mixture.
In both steps, the contact of the purifying liquids with crude or unpurified natural gas is important. By enhancing the contact area of the liquids with the gas, the efficiency and rate of purification would increase. Further, the domain size of the liquids is decreased by discretizing the liquids into micronized droplets, thus enhancing mass transport of gases (in particular gases to be absorbed) into the sorbent. This would allow the usage of shorter purification columns/contactors and higher gas flow rates. Also, energy could be saved because there would be a decreased need for agitation of viscous liquids like diethanolamine (DEA) or monoethanolamine (MEA), which are widely used in gas sweetening processes.
In industrial gas purification set-ups, neat MEA is rarely used. Most commonly, a 20-30 wt % aqueous solution of MEA is utilized instead. This is due to the high viscosity of neat MEA (approximately 24 times that of water at 20° C.) as well as its corrosive nature. High liquid viscosity results in difficulty of liquid agitation and transport through the gas contactors. Neat DEA and triethanolamine (TEA) have even higher viscosity than that of MEA, and their agitation for enhanced surface interaction with the gases demands even more energy.